The present invention relates to an apparatus for determining reflectivity of a laser mirror by using a CO.sub.2 laser beam in order to detect any possible crack or defect on the mirror surface.
Heretofore, any possible crack or defect on a laser mirror has not been detected, since there was no means for determining the reflectivity of the mirror. As a result, the mirror may crack, where the mirror material is not uniform. Furthermore, the coating on the mirror may locally peel off under an intense working condition.
When the mirror becomes defective due to foreign substances entering in the working stage such as fumes or dust, such defective mirror can not be detected and is thereby continuously used. Over a period of time, the mirror will be further damaged due to accumulated defects amounting from the original damage thereof. In addition, laser radiation will be reduced due to the crack or defect on the mirror, thereby reducing the efficiency of the mirror, and thus, deteriorating the quality of obtained product.